The present invention relates to the formation of high resilience polyurethane foam.
It is well known to the art that urethane polymers are provided by the reaction of organic polyisocyanates and active hydrogen-containing organic compounds such as, for example, polyether polyols. It is also well known that the reaction is usually effected in the presence of one or more activators and that blowing action is provided when cellular products are desired. In producing conventional flexible polyether urethane foam, the rate of reaction and heat generated by the exothermic reaction between the polyisocyanate and polyether polyol is sufficient to cure the center of the foam product but the surface temperature usually does not rise high enough to cure the outside rapidly. Consequently, extended high temperature post cure treatment is necessary in commercial practice to provide a foamed product of satisfactory overall properties.
A relatively recent advance in polyurethane foam technology is the advent of reaction mixtures having a sufficiently high reactivity to provide faster and more complete reactions during polymer formation and expansion. As a result, overall processing time including high temperature post curing, if any, is substantially reduced. Basically, the more highly exothermic nature of such reaction mixtures is provided by the employment of polyether polyols having a high content of primary hydroxyl groups. Such foams are especially desirable for cushioning applications in view of their excellent physical properties. Among these properties are reduced combustibility relative to conventional polyether foam, low flex fatigue which means long life as a cushioning material, and high resilience which is usually from about 55 to about 70 percent, as measured by standard test procedure ASTM D-1564-69. In view of this latter characteristic, such foams are commonly referred to as "high resilience" foam, and previously as "cold cure" foam.
Because of the rapid buildup of gel strength of high resilience foam systems, the foam can sometimes be provided without a surfactant. Typically, however, high resilience foams produced without a surfactant or stabilizer have very irregular cell structure. It is usually desirable, therefore, to include a silicone surfactant as an additional component of high resilience foam formulations in order to control cell uniformity and to minimize the tendency of the foam to settle. In general surfactants required for stabilization of conventional flexible polyether foam are unsatisfactory for high resilience foam because they overstabilize, causing extremely tight foam and excessive shrinkage. If the problem is sought to be corrected by reducing the concentration of such surfactants to a level which eliminates shrinkage, the cells are no longer stabilized satisfactorily and the foam structure becomes irregular and coarse.
It is known that specific low viscosity unmodified dimethylsilicone oils having a narrow low molecular weight distribution are useful stabilizers for high resilience foam, but in general have various disadvantages. For example, the very low use levels at which they give the best foam properties, about 0.05 to 0.10 parts per 100 parts of polyol, create metering and pumping problems, while relatively high concentrations of these oils adversely affect the physical properties of the foam. Moreover, solvents for such oils that are non-reactive with the foam ingredients, e.g. alkanes, hexamethyldisiloxane, and the like, adversely affect the foam's physical properties in proportion to their concentration and generally create flammability hazards, while isocyanate reactive diluents, such as polyether triols, and the like, which do not significantly change the foam's properties, inasmuch as they become part of the foam structure, are not satisfactory solvents for dimethylsilicone oils, thus in general not enough oil can be dissolved to provide foam stabilization at practical solution concentrations. Further, high resilience foam systems are adversely affected by dimethylsilicones having more than about ten dimethylsiloxy units per chains. For example, only five or ten weight percent of such species in a dimethyl oil appreciably degrade foam physical properties and even cause foam shrinkage.
Among other more successful classes of surfactants for high resilience foam are: (1) the relatively low molecular weight polysiloxane-polyoxyalkylene copolymers described in U.S. Pat. No. 3,741,917; (2) the particular class of aralkyl-modified siloxanes described in U.S. Pat. No. 3,839,384; (3) the cyanoalkoxy- and cyanoalkoxy-modified siloxanes described in U.S. Pat. No. 3,905,924; and (4) the cyanoalkoxyalkyl- and cyanoalkoxyalkoxy-modified siloxanes described in Belgium Pat. No. 809,979.
It is a principal object of this invention to provide a process for preparing high resilience polyether polyurethane foam employing tertiary alcohol modified siloxane surfactants. Various other objects and advantages of this invention will become readily apparent to those skilled in the art from the accompanying description and disclosure.